Psoriasis is a chronic, genetically-influenced, remitting and relapsing scaly and inflammatory skin disorder that affects 1 to 3 percent of the world's population. It is characterized by erythematous, sharply demarcated papules and rounded plaques, covered by silvery micaceous scale. The skin lesions of psoriasis are variably pruritic. There are several types of psoriasis, including plaque, pustular, guttate and arthritic variants. There is at present no cure for psoriasis, but rather only suppressive therapy (Greaves and Weinstein, 1995, Drug Therapy, 332: 581-588).
The disease appears at two different ages. The premature disease presentation (type 1), with a peak between 15 and 35 years of age, is the most frequent and is normally associated to family records. The late disease presentation (type 2) is presented in a peak of the ages between the 55 and the 60 years.
It is not known what causes psoriasis, although there is evidence of a genetic predisposition and an autoimmune etiology. Onset may be triggered by systemic infections such as strep throat, skin injury, vaccinations, and certain oral medications such as steroids. Subsequently, the immune system is thought to induce inflammation and excessive skin cell reproduction, which can be exacerbated by additional factors such as stress and diet.
The goal of current treatments has been to decrease the severity and extent of psoriasis to the point at which it no longer interferes substantially with the patient's occupation, well-being, or personal or social life. The initial treatment for stable plaque psoriasis of any severity is topical. In patients in which more than 20 percent of the skin is affected, however, topical treatment alone may be impractical and systemic therapy may also be indicated at the outset.
The topical treatment for plaque psoriasis incorporates the use of emollients, keratolytic agents, coal tar, anthralin, corticosteroids of medium to strong potency, and calpotriene. All of these treatments have variable efficacy, fail to prevent frequent relapses of the disease, exhibit side effects, and pose cosmetic problems of their own. The use of steroids may also lead to resistance, rendering subsequent steroid treatment ineffective.
Systemic treatment has been used in patients with physically, socially, or economically disabling psoriasis that has not responded to topical treatment. The choices to date have been phototherapy or systemic drug therapy. Generally, systemic treatment has employed phototherapy with Ultraviolet B irradiation, photo chemotherapy which combines the photosensitizing drug methoxsalen with Ultraviolet A phototherapy (PUVA), methotrexate, etretinate, systemic corticosteroids, and cyclosporine. Each of these systemic treatments has variable efficacy and undesired side effects, and some of them are very toxic and present frequent relapses of the disease. For example, long term use of phototherapies may prematurely age the skin and increase the incidence of skin cancers. The use of methotrexate requires careful monitoring to avoid liver damage. Use of oral retinoids must be carefully controlled in women because of the potential for severe birth defects. This risk extends for years after the use of the drug has been terminated. Cyclosporine, an immunosuppresant, is reserved for patients that have failed other internal treatments, or for whom the other internal treatments are contraindicated. Rotating between therapies, and combinations of topical medications with phototherapies, have also been found to be useful regimens in the treatment of psoriasis.
Accordingly, there is at present an urgent need for an effective psoriasis treatment that avoids the disadvantages associated with the currently available topical or systemic treatments, with improved efficacy, safety, and side effect profiles.
It is an object of the present invention to provide an effective treatment of psoriasis, showing clinical benefit.
In particular, it is an object of the invention to provide dosages and schedules of compounds that can be used for psoriasis therapy in humans, avoiding toxicities while maintaining the desired effects.
It is yet another object of the invention to provide new products, for administration in the treatment of psoriasis.